The invention relates to a switching arrangement for full-wave power control comprising a triac, the control electrode of which is preceded by a trigger diode, the control voltge being taken from an RC section having at least one potentiometer, which, as a function of the position of the potentiometer, effects a phase shift in the firing time. Such circuits are used, for example, for controlling the brightness in lighting systems or for adjusting the rotational speed, particularly of electric tools.
Firing circuits for triacs as full-wave power controllers are known, for example from "Halbleiter-Schaltungstechnik" (Semiconductor Circuit Engineering, U. Tietze and Ch. Schenk, Springer-Verlag, 1971, pages 577 at seq. or from "Thyristoren und Triacs" (Thyristors and Triacs), Ing. (grad.) Heinz Richter, Franckh'sche Verlagshandlung W. Keller & Co., 1969, page 52 and 53. The efforts to improve such switching arrangements were previously mainly directed towards reducing the switching hysteresis. However, in series production the main disadvantage which becomes noticeable is that the angle of current flow is highly dependent on mains voltage, with a particular potentiometer setting. For this reason, it is difficult to calibrate the circuit, even before installation into, for example, a hand-drill, in such a manner that the armture of the motor is audibly rotating in the drilling start position of the potentiometer (largest resistance which can be set), but, on the other hand, is still rotating as slowly as is desirable to start drilling. Incidentally, the development of solutions free of switching thyristors has led to relatively elaborate switching arrangements with many individual components.